Question

For air flow over the wing of an airplane, which of the following definitions of Reynolds number will let you determine the drag force on the wing? U₀ is the free stream velocity, L is the length of the wing in the flow direction, B is the width of the wing, x is the distance along the wing from the leading edge, and t is the thickness of the wing.

a. U₀L/v
b. U₀B/v
c. U₀x/v
d. U₀t/v

Answer 1

Option a. The correct Reynolds number definition to determine the drag force on an airplane's wing is U₀L/ν. It uses the length of the wing in the flow direction (L) as the characteristic length, with 'L' being the chord length of the wing.

Step-by-step explanation:

To determine the drag force on the wing of an airplane using the Reynolds number, you would use the definition of Reynolds number as U₀L/ν, where U₀ is the free stream velocity, L is the characteristic length of the wing in the flow direction, and ν is the kinematic viscosity of air. The choice of characteristic length typically depends on the geometry of the object and for wings, it is their chord length which is analogous to the 'L' in the equation.

The width B, distance along the wing x, and thickness t of the wing would not typically be used as the characteristic length for this purpose. Once you have calculated the Reynolds number, you can then determine whether the flow is laminar or turbulent, which in turn affects the drag on the wing.